Congratulations! What is your budget? While there are some deals to be had in Allston/Brighton, there are a lot of pitfalls to the area. First off, the B line is a major pain, and actually not that close to Simmons, and a good hike to Emerson depending on where his classes are. Secondly, student-friendly means... student-friendly. Tons of annoying, loud students. Yuck.
I recommend looking in Mission Hill. It's a hop skip and a jump to Simmons, and then your boyfriend can take the 39 bus to Hynes and walk over to Emerson, or the E line to the 1 bus if he doesn't want to do any walking whatsoever.
The Fenway area, of course, is an option, but it's not going to come so cheap. But you won't beat it for convenience in terms of getting to school, and it's centrally located to both schools.
And then, if you don't mind being a hair further out, consider Jamaica Plain, a neighborhood that a lot of people are just in love with. And it's super cheap (all things being relative). The 39 bus will take you into JP and goes right near Simmons and into Back Bay.